Microcomputer having an oscillator part with variable driving ability

A microcomputer, comprising:

• driving ability selecting means responsive to an external signal for selecting the driving ability of an oscillator generating a clock signal;
• an oscillator circuit part, said part including a driving ability changing means coupled to said selecting means for changing the driving ability of the oscillator circuit;
• count means coupled to said oscillator circuit for counting clock signal pulses;
• signal output means coupled to, and responsive to an output signal from, said count means for outputting a predetermined signal in response to said count means counting a predetermined value;
• internal clock supply means coupled to said oscillator circuit and to said signal output means for supplying an internal clock signal in response to said predetermined signal;
• a logic circuit coupled to said driving ability selecting means and to said signal output means, and responsive to a signal related to the predetermined signal and the content of said driving ability selecting means, for providing a logic circuit output signal;
• and
• control means coupled to said logic circuit for controlling said driving ability changing means in response to said logic circuit output signal, so that a large driving ability is obtained during the period from the initiation of oscillation to the initiation of the supply of the internal clock signal and that a driving ability in accordance with the content of said driving ability selecting means is obtained in relation to the initiation of the supply of the internal clock signal.